Droplet generator and method of servicing a photolithographic tool

ABSTRACT

A photolithographic apparatus includes a droplet generator, a droplet generator maintenance system, and a controller communicating with the droplet generator maintenance system. The droplet generator maintenance system operatively communicates with the droplet generator, a coolant distribution unit, a gas supply unit, and a supporting member. The gas supply unit includes a heat exchange assembly and an air heating assembly. The coolant distribution unit is configured to control the temperature of the droplet generator within the acceptable droplet generator range.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/187,272 filed Feb. 26, 2021, now U.S. Pat. No. 11,275,317, the entirecontent of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to a droplet generator for an extreme ultravioletimaging tool and a method of servicing the extreme ultraviolet imagingtool.

BACKGROUND

As consumer devices have gotten smaller and smaller in response toconsumer demand, the individual components of these devices havenecessarily decreased in size as well. Semiconductor devices, which makeup a major component of devices such as mobile phones, computer tablets,and the like, have been pressured to become smaller and smaller, with acorresponding pressure on the individual devices (e.g., transistors,resistors, capacitors, etc.) within the semiconductor devices to also bereduced in size. The decrease in size of devices has been met withadvancements in semiconductor manufacturing techniques such aslithography.

For example, the wavelength of radiation used for lithography hasdecreased from ultraviolet to deep ultraviolet (DUV) and, more recentlyto extreme ultraviolet (EUV). Further decreases in component sizerequire further improvements in resolution of lithography which areachievable using extreme ultraviolet lithography (EUVL). EUVL employsradiation having a wavelength of about 1-100 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 shows an extreme ultraviolet lithography tool according to anembodiment of the disclosure.

FIG. 2 shows a schematic diagram of a detail of an extreme ultravioletlithography tool according to an embodiment of the disclosure.

FIGS. 3A and 3B show a schematic diagram of a droplet generatoraccording to an embodiment of the disclosure.

FIG. 4A shows a detailed view of a coolant distribution unit and anair-cooled droplet generator according to an embodiment of thedisclosure.

FIGS. 4B and 4C show an embodiment of the coolant distribution unit andthe air-cooled droplet generator according to an embodiment of thedisclosure.

FIG. 5 shows a detailed view of a droplet generator maintenance systemincluding a dual gas supply unit according to an embodiment of thedisclosure.

FIG. 6A schematically illustrates the operation of the dual gas supplyunit according to an embodiment of the disclosure.

FIG. 6B schematically illustrates an operation of servicing an extremeultraviolet lithography tool by using a heat exchange assembly.

FIG. 6C schematically illustrates an operation of servicing an extremeultraviolet lithography tool using an air heating assembly.

FIG. 6D schematically illustrates an operation of servicing an extremeultraviolet lithography tool using a gas.

FIG. 7 is a flowchart of a method of servicing an extreme ultravioletlithography tool according to an embodiment of the disclosure.

FIG. 8 illustrates a flow chart of a method for controlling a dropletgenerator maintenance system to perform a droplet generator coolingprocess in accordance with an embodiment of the present disclosure.

FIG. 9 illustrates a flow chart of a method for controlling the dropletgenerator maintenance system to perform a droplet generator heatingprocess in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.”

The present disclosure is generally related to extreme ultraviolet (EUV)lithography systems and methods. More particularly, it is related toextreme ultraviolet lithography (EUVL) tools and methods of servicingthe tools. In an EUVL tool, a laser-produced plasma (LPP) generatesextreme ultraviolet radiation which is used to image a photoresistcoated substrate. In an EUV tool, an excitation laser heats metal (e.g.,tin, lithium, etc.) target droplets in the LPP chamber to ionize thedroplets to plasma which emits the EUV radiation. For reproduciblegeneration of EUV radiation, the target droplets arriving at the focalpoint (also referred to herein as the “zone of excitation”) have to besubstantially the same size and arrive at the zone of excitation at thesame time as an excitation pulse from the excitation laser arrives.Thus, stable generation of target droplets that travel from the targetdroplet generator to the zone of excitation at a uniform (orpredictable) speed contributes to efficiency and stability of the LPPEUV radiation source.

FIG. 1 is a schematic view of an EUV lithography tool with a laserproduced plasma (LPP) based EUV radiation source, constructed inaccordance with some embodiments of the present disclosure. The EUVlithography system includes an EUV radiation source 100 to generate EUVradiation, an exposure device 200, such as a scanner, and an excitationlaser source 300. As shown in FIG. 1, in some embodiments, the EUVradiation source 100 and the exposure device 200 are installed on a mainfloor MF of a clean room, while the excitation laser source 300 isinstalled in a base floor BF located under the main floor MF. Each ofthe EUV radiation source 100 and the exposure device 200 are placed overpedestal plates PP1 and PP2 via dampers DP1 and DP2, respectively. TheEUV radiation source 100 and the exposure device 200 are coupled to eachother by a coupling mechanism, which may include a focusing unit.

The EUV lithography tool is designed to expose a resist layer by EUVlight (also interchangeably referred to herein as EUV radiation). Theresist layer is a material sensitive to the EUV light. The EUVlithography system employs the EUV radiation source 100 to generate EUVlight, such as EUV light having a wavelength ranging between about 1 nmand about 100 nm. In one particular example, the EUV radiation source100 generates an EUV light with a wavelength centered at about 13.5 nm.In the present embodiment, the EUV radiation source 100 utilizes amechanism of laser-produced plasma (LPP) to generate the EUV radiation.

The exposure device 200 includes various reflective optic components,such as convex/concave/flat mirrors, a mask holding mechanism includinga mask stage, and wafer holding mechanism. The EUV radiation EUVgenerated by the EUV radiation source 100 is guided by the reflectiveoptical components onto a mask secured on the mask stage. In someembodiments, the mask stage includes an electrostatic chuck (e-chuck) tosecure the mask.

FIG. 2 is a simplified schematic diagram of a detail of an extremeultraviolet lithography tool according to an embodiment of thedisclosure showing the exposure of photoresist coated substrate 210 witha patterned beam of EUV light. The exposure device 200 is an integratedcircuit lithography tool such as a stepper, scanner, step and scansystem, direct write system, device using a contact and/or proximitymask, etc., provided with one or more optics 205 a, 205 b, for example,to illuminate a patterning optic 205 c, such as a reticle, with a beamof EUV light, to produce a patterned beam, and one or more reductionprojection optics 205 d, 205 e, for projecting the patterned beam ontothe substrate 210. A mechanical assembly (not shown) may be provided forgenerating a controlled relative movement between the substrate 210 andpatterning optic 205 c. As further shown in FIG. 2, the EUVL toolincludes an EUV light source 100 including an EUV light radiator ZEemitting EUV light in a chamber 105 that is reflected by a collector 110along a path into the exposure device 200 to irradiate the substrate210.

As used herein, the term “optic” is meant to be broadly construed toinclude, and not necessarily be limited to, one or more components whichreflect and/or transmit and/or operate on incident light, and includes,but is not limited to, one or more lenses, windows, filters, wedges,prisms, grisms, gradings, transmission fibers, etalons, diffusers,homogenizers, detectors and other instrument components, apertures,axicons and mirrors including multi-layer mirrors, near-normal incidencemirrors, grazing incidence mirrors, specular reflectors, diffusereflectors and combinations thereof. Moreover, unless otherwisespecified, neither the term “optic”, as used herein, are meant to belimited to components which operate solely or to advantage within one ormore specific wavelength range(s) such as at the EUV output lightwavelength, the irradiation laser wavelength, a wavelength suitable formetrology or any other specific wavelength.

Because gas molecules absorb EUV light, the lithography system for theEUV lithography patterning is maintained in a vacuum or a-low pressureenvironment to avoid EUV intensity loss.

In the present disclosure, the terms mask, photomask, and reticle areused interchangeably. In the present embodiment, the patterning optic205 c is a reflective mask. In an embodiment, the reflective mask 205 cincludes a substrate with a suitable material, such as a low thermalexpansion material or fused quartz. In various examples, the materialincludes TiO₂ doped SiO₂, or other suitable materials with low thermalexpansion. The reflective mask 205 c includes multiple reflectivemultiple layers (ML) deposited on the substrate. The ML includes aplurality of film pairs, such as molybdenum-silicon (Mo/Si) film pairs(e.g., a layer of molybdenum above or below a layer of silicon in eachfilm pair). Alternatively, the ML may include molybdenum-beryllium(Mo/Be) film pairs, or other suitable materials that are configured tohighly reflect the EUV light. The mask 205 c may further include acapping layer, such as ruthenium (Ru), disposed on the ML forprotection. The mask further includes an absorption layer, such as atantalum boron nitride (TaBN) layer, deposited over the ML. Theabsorption layer is patterned to define a layer of an integrated circuit(IC). Alternatively, another reflective layer may be deposited over theML and is patterned to define a layer of an integrated circuit, therebyforming an EUV phase shift mask.

In various embodiments of the present disclosure, the photoresist coatedsubstrate 210 is a semiconductor wafer, such as a silicon wafer or othertype of wafer to be patterned.

The EUVL tool further include other modules or is integrated with (orcoupled with) other modules in some embodiments.

As shown in FIG. 1, the EUV radiation source 100 includes a targetdroplet generator 115 and a LPP collector 110, enclosed by a chamber105. In various embodiments, the target droplet generator 115 includes areservoir (see FIG. 3A) to hold a source material and a nozzle 120through which target droplets DP of the source material are suppliedinto the chamber 105.

In some embodiments, the target droplets DP are droplets of tin (Sn),lithium (Li), or an alloy of Sn and Li. In some embodiments, the targetdroplets DP each have a diameter in a range from about 10 microns (μm)to about 100 μm. For example, in an embodiment, the target droplets DPare tin droplets, having a diameter of about 10 μm to about 100 μm. Inother embodiments, the target droplets DP are tin droplets having adiameter of about 25 μm to about 50 μm. In some embodiments, the targetdroplets DP are supplied through the nozzle 120 at a rate in a rangefrom about 50 droplets per second (i.e., an ejection-frequency of about50 Hz) to about 50,000 droplets per second (i.e., an ejection-frequencyof about 50 kHz). In some embodiments, the target droplets DP aresupplied at an ejection-frequency of about 100 Hz to a about 25 kHz. Inother embodiments, the target droplets DP are supplied at an ejectionfrequency of about 500 Hz to about 10 kHz. The target droplets DP areejected through the nozzle 120 and into a zone of excitation ZE at aspeed in a range of about 10 meters per second (m/s) to about 100 m/s insome embodiments. In some embodiments, the target droplets DP have aspeed of about 10 m/s to about 75 m/s. In other embodiments, the targetdroplets have a speed of about 25 m/s to about 50 m/s.

Referring back to FIG. 1, an excitation laser LR2 generated by theexcitation laser source 300 is a pulse laser. The laser pulses LR2 aregenerated by the excitation laser source 300. The excitation lasersource 300 may include a laser generator 310, laser guide optics 320 anda focusing apparatus 330. In some embodiments, the laser source 310includes a carbon dioxide (CO₂) or a neodymium-doped yttrium aluminumgarnet (Nd:YAG) laser source with a wavelength in the infrared region ofthe electromagnetic spectrum. For example, the laser source 310 has awavelength of 9.4 μm or 10.6 μm, in an embodiment. The laser light LR1generated by the laser generator 310 is guided by the laser guide optics320 and focused into the excitation laser LR2 by the focusing apparatus330, and then introduced into the EUV radiation source 100.

In some embodiments, the excitation laser LR2 includes a pre-heat laserand a main laser. In such an embodiment, the pre-heat laser pulse(interchangeably referred to herein as the “pre-pulse) is used to heat(or pre-heat) a given target droplet to create a low-density targetplume with multiple smaller droplets, which is subsequently heated (orreheated) by a pulse from the main laser, generating increased emissionof EUV light.

In various embodiments, the pre-heat laser pulses have a spot size about100 μm or less, and the main laser pulses have a spot size in a range ofabout 150 μm to about 300 μm. In some embodiments, the pre-heat laserand the main laser pulses have a pulse-duration in the range from about10 ns to about 50 ns, and a pulse-frequency in the range from about 1kHz to about 100 kHz. In various embodiments, the pre-heat laser and themain laser have an average power in the range from about 1 kilowatt (kW)to about 50 kW. The pulse-frequency of the excitation laser LR2 ismatched with the ejection-frequency of the target droplets DP in anembodiment.

The laser light LR2 is directed through windows (or lenses) into thezone of excitation ZE. The windows adopt a suitable materialsubstantially transparent to the laser beams. The generation of thepulse lasers is synchronized with the ejection of the target droplets DPthrough the nozzle 120. As the target droplets move through theexcitation zone, the pre-pulses heat the target droplets and transformthem into low-density target plumes. A delay between the pre-pulse andthe main pulse is controlled to allow the target plume to form and toexpand to an optimal size and geometry. In various embodiments, thepre-pulse and the main pulse have the same pulse-duration and peakpower. When the main pulse heats the target plume, a high-temperatureplasma is generated. The plasma emits EUV radiation EUV, which iscollected by the collector mirror 110. The collector 110 furtherreflects and focuses the EUV radiation for the lithography exposingprocesses performed through the exposure device 200. The droplet catcher125 is used for catching excessive target droplets. For example, sometarget droplets may be purposely missed by the laser pulses.

Referring back to FIG. 1, the collector 110 is designed with a propercoating material and shape to function as a mirror for EUV collection,reflection, and focusing. In some embodiments, the collector 110 isdesigned to have an ellipsoidal geometry. In some embodiments, thecoating material of the collector 100 is similar to the reflectivemultilayer of the EUV mask. In some examples, the coating material ofthe collector 110 includes a ML (such as a plurality of Mo/Si filmpairs) and may further include a capping layer (such as Ru) coated onthe ML to substantially reflect the EUV light. In some embodiments, thecollector 110 may further include a grating structure designed toeffectively scatter the laser beam directed onto the collector 110. Forexample, a silicon nitride layer is coated on the collector 110 and ispatterned to have a grating pattern.

In such an EUV radiation source, the plasma caused by the laserapplication creates physical debris, such as ions, gases and atoms ofthe droplet, as well as the desired EUV radiation. It is necessary toprevent the accumulation of material on the collector 110 and also toprevent physical debris exiting the chamber 105 and entering theexposure device 200.

As shown in FIG. 1, in the present embodiment, a buffer gas is suppliedfrom a first buffer gas supply 130 through the aperture in collector 110by which the pulse laser is delivered to the tin droplets. In someembodiments, the buffer gas is H₂, He, Ar, N₂ or another inert gas. Incertain embodiments, H₂ used as H radicals generated by ionization ofthe buffer gas can be used for cleaning purposes. The buffer gas canalso be provided through one or more second buffer gas supplies 135toward the collector 110 and/or around the edges of the collector 110.Further, the chamber 105 includes one or more gas outlets 140 so thatthe buffer gas is exhausted outside the chamber 105.

Hydrogen gas has low absorption to the EUV radiation. Hydrogen gasreaching the coating surface of the collector 110 reacts chemically witha metal of the droplet forming a hydride, e.g., metal hydride. When tin(Sn) is used as the droplet, stannane (SnH₄), which is a gaseousbyproduct of the EUV generation process, is formed. The gaseous SnH₄ isthen pumped out through the outlet 140.

FIG. 3A schematically illustrates the components of the dropletgenerator 115. As shown in FIG. 3A, the droplet generator 115 includes areservoir 150 holding a fluid 145, e.g. molten tin, under pressure P.The reservoir 150 is formed with an orifice 155 allowing the pressurizedfluid 145 to flow through the orifice 155 establishing a continuousstream which subsequently breaks into a plurality of droplets DP1, DP2exiting the nozzle 120.

The target droplet generator 115 shown further includes a sub-systemproducing a disturbance in the fluid 145 having an electro-actuatableelement 160 that is operably coupled with the fluid 145 and a signalgenerator 165 driving the electro-actuatable element 160 in someembodiments. In some embodiments, the electro-actuatable element 160 isa piezoelectric actuator that applies vibration to the fluid. In someembodiments, the electro-actuatable element 160 is an ultrasonictransducer or a megasonic transducer.

When the reservoir 150 becomes empty or the remaining fluid is less thana threshold level, a maintenance operation is performed. Duringmaintenance or servicing, the nozzle 120 is cooled down. If the nozzle120 cools down, it will have to be brought back up to operatingtemperature prior to restarting the droplet generator 115. This canincrease downtime during maintenance or servicing. Further, a change intemperature of the nozzle 120 changes the droplet quality. The dropletgenerator 115 may need to be recalibrated after it cools down, whichfurther increase tool downtime during maintenance and servicing.

As shown in FIG. 3B, a heating element 505 is connected to the nozzle120 to maintain the nozzle 120 at the operating temperature duringmaintenance and servicing. In some embodiments, the temperature of thenozzle 120 is maintained at about 250° C. during maintenance andservicing. The heating element 505 is connected to an uninterruptiblepower supply (UPS) 510 to continuously provide power to the heatingelement 505 during maintenance or servicing. In some embodiments, theuninterruptible power supply 510 is connected to a power distributionunit (PDU) 515 of the EUVL tool. In some embodiments, theuninterruptible power supply 510 is connected to the controller 180. Insome embodiments, the controller 180 closes the isolation valve 185 andactivates the uninterruptible power supply 510 substantiallysimultaneously. In some embodiments, the controller 180 also opens avalve from the inert gas source (not shown) to cause inert gas to flowinto the nozzle 120 through an inlet. In some embodiments, thecontroller 180 closes the isolation valve 185, initiates inert gas flowto the nozzle 120, and activates the uninterruptible power supply 510 topower the heating element 505 substantially simultaneously. In someembodiments, the controller 180 communicates with a droplet generatormaintenance (DGM) system 1000.

FIG. 4A shows the droplet generator maintenance (DGM) system 1000including a coolant distribution unit 1100 and an air-cooled dropletgenerator 115. The coolant distribution unit 1100 includes a booster box1102 and a pressurized gas 1090. In some embodiments, the gas is N₂, Ar,He, H₂ or mixture thereof. In some embodiments, the gas is a forming gas(i.e. a mixture of H₂ and N₂). In some embodiments, the forming gascontains from about 5 mol % H₂ to about 15 mol % H₂ in N₂. The coolantdistribution unit 1100 is connected to the droplet generator 115 using asupply manifold 1112, a return manifold 1113, a supply line 1114, areturn line 1115, a three-way valve 1116 and a droplet line 1117 in someembodiments. According to an embodiment of this disclosure, the dropletgenerator 115 is connected to the booster box 1102 via the supplymanifold 1112, the supply line 1114 and the droplet line 1117 to receivea pressurized gas 1090 from the booster box 1102 to the orifice 155 ofthe droplet generator 115. In some embodiments, the droplet generator1115 is also connected to the return manifold 1113 via the droplet line1117 and the return line 1115 to exhaust hot pressurized gas 1091 fromthe orifice 155 of the droplet generator 115. In some embodiments, thethree-way valve 1116 functions as a bridge between the supply line 1114and the return line 1115 from the droplet line 1117. A plurality ofquick connect couplings may be used as an interface among the supplyline 1114, the return line 1115, the three-way valve 1116 and thedroplet line 1117. By way of example, the plurality of quick connectcouplings include various types of commercially available couplings.

In some embodiments, the droplet generator 115 includes an airconditioning device 1104 (e.g., external fans or blowers) to provide aforced air flow from top to bottom to cool the temperature of thedroplet generator 115. In such an embodiment, the forced air flow by theair conditioning device 1104 passes through an air flow contact area1106 of the droplet generator 115. Such forced air flow may pass throughabout 30% of a total surface area 1108 of the droplet generator 115. Inaddition, the forced air flow by the air conditioning device 1104 alsoincludes exhausted hot air from a hot surface of the droplet generator115. Faster recirculating of the air flow for the droplet generatorswithin the LPP is often very complex in nature. Due to an airdistribution by the air conditioning device 1104 within the current EUVscanner and increasing air flow requirements for the droplet generators,the temperature of the droplet generator 115 can get significantlyhigher than desired.

Clean dry air (CDA) is supplied to the booster box 1102 of the coolantdistribution unit 1100. In some embodiments, CDA includes N₂ gas. Insome embodiments, the CDA is introduced when it is necessary to providepressure to the droplet generator. In some embodiments, the CDA isintroduced at a pressure between a first pressure (filling pressure tothe droplet generator) and a second pressure (exhaust pressure from thedroplet generator). In some embodiments, the first pressure (fillingpressure to the droplet generator) for the pressurizing operation is ina range from about 700 Pa to about 900 Pa. In some embodiments, thefirst pressure is about 800 Pa. In some embodiments, the second pressure(exhaust pressure) for the flushing operation is in a range from about300 Pa to about 500 Pa. In some embodiments, the second pressure isabout 400 Pa. In some embodiments, the second pressure for the flushingoperation is in a range from about 40% to about 60% of the firstpressure. In some embodiments, the second pressure is in a range fromabout 30% to about 70% of the first pressure.

FIGS. 4B and 4C show an embodiment of the coolant distribution unit 1100configured to control the temperature of the air-cooled dropletgenerator 115. As shown in FIG. 4B, the booster box 1102 is arranged toreceive room temperature gas 1122. In some embodiments, the gas 1122includes an ambient gas. When the gas 1122 is received into the boosterbox 1102, the coolant distribution unit 1100 is configured to pressurizethe booster box 1102 using the clean dry air (CDA). In some embodiments,compressed CDA is provided to the booster box 1102 to allow a pneumaticconnection between a CDA line and the supply manifold 1112 to change aconfiguration such that the gas 1122 in the supply manifold 1112 getspressurized. The coolant distribution unit 1100 controls the three-wayvalve 1116 to provide the gas 1122 in the booster box 1102 through thesupply manifold 1112 and the three-way valve 1116 and to introduce thegas 1122 into the orifice 155 of the droplet generator 115. When theambient gas 1122 is received inside the orifice 155 of the dropletgenerator 115, the gas 1122 reduces the temperature of the orifice 155by absorbing heat within the orifice 155 of the droplet generator 115and becomes hot gas 1123.

FIG. 4C shows the coolant distribution unit 1100 that dissipates heatfrom the orifice 155 of the droplet generator 115. The coolantdistribution unit 1100 of this embodiment is configured to close asupply end 1116S of the three-way valve 1116, and the booster box 1102is depressurized. When the supply end 1116S of the three-way valve 1116is closed from the booster box 1102, the coolant distribution unit 1100is configured to open the return manifold 1113 and the return line 1115so that heat accumulated inside the droplet generator 115 can bedissipated by the hot gas 1123.

When the hot gas 1123 is exhausted from the orifice 155 of the dropletgenerator 115, the temperature of the droplet generator is measured todetermine whether the droplet generator DG is within an acceptable coldtemperature range. If the measured temperature of the droplet generatorDG is not within the acceptable temperature range, configurableparameters of the coolant distribution unit 1100 connected areautomatically adjusted to repeat the process shown in FIGS. 4B and 4C,so as to reduce the temperature of the droplet generator DG within theacceptable temperature range. In some embodiments, the acceptable coldtemperature range of the DG ranges is from about 5° C. to about 50° C.

As shown in FIG. 5, the droplet generator maintenance system 1000further includes a gas supply unit 1200. In some embodiments, the gassupply unit 1200 includes a heat exchange assembly 1300. The heatexchange assembly 1300 is configured to extract heat from hot gas purgedfrom the droplet generator DG to decrease the temperature of the gasprior to entering the booster box 1102 of the coolant distribution unit1100. The heat exchange assembly 1300 includes a heat exchanger 1320, afacility coolant loop 1340 and a system coolant gas line 1360. When theheat exchange assembly 1300 is operatively communicating with the LPP,the facility coolant loop 1340 receives chilled facility coolant from acoolant source and passes at least a portion of the coolant through theheat exchanger 1320. The system coolant gas line 1360 receives a purgedhot gas and provides a heat-exchanged cold gas in a temperature rangefrom about −40° C. to about 0° C. to the booster box 1102 of the coolantdistribution unit 1100. In such an embodiment, the droplet generator 115is connected to the booster box 1102 via the supply manifold, the supplyline and the droplet line and receives the heat-exchanged cold gas fromthe booster box into the orifice of the droplet generator to cool thetemperature in the orifice of the droplet generator 115.

FIG. 6A schematically illustrates a variation in the gas supply unit1200 used to heat the droplet generator DG. The gas supply unit 1200further includes an air heating assembly 1400 as shown in FIG. 6A. Insome embodiments, the air heating assembly 1400 includes an air heater1420. The air heating assembly 1400 is configured to provide heat tocold gas 1402 and to increase the temperature of the gas prior toentering the booster box 1102 of the coolant distribution unit 1100. Theair heating assembly 1400 includes the air heater 1420 and a systemheated gas line 1460. When the air heating assembly 1400 is operativelycommunicating with the LPP, the air heating assembly 1400 receives thecold gas 1402 from a gas source and passes at least a portion of andthrough the air heater 1420. The system heated gas line 1460 receives acold gas purged from the droplet generator DG and provides a hot gas tothe booster box 1102 of the coolant distribution unit 1100 to heat thedroplet generator DG to its operating temperature. In such anembodiment, the droplet generator 115 is connected to the booster box1102 via the supply manifold, the supply line and the droplet line andreceives the hot gas from the booster box into the orifice of thedroplet generator to increase the temperature in the orifice of thedroplet generator 115. In some embodiments, the hot gas provided to thedroplet generator DG is heated to a temperature ranging from about 235°C. to about 300° C.

In some embodiments, the gas supply unit 1200 further includes a dualtemperature three-way valve 1216 as a bridge between the system coolantgas line 1360 and the system heated gas line 1460 to the booster box1102. A plurality of quick connect couplings may be used as an interfaceamong the system coolant gas line 1360, system heated gas line 1460, thebooster box 1102 and the dual temperature three-way valve 1216.

FIGS. 6B, 6C and 6D schematically illustrate an operation of servicingan extreme ultraviolet lithography tool. As shown in FIG. 6B, when thedroplet generator maintenance starts, in some embodiments, the dropletgenerator maintenance (DGM) system 1000 turns on the heat exchanger 1320of the heat exchange assembly 1300 and switches the dual temperaturethree-way valve 1216 to the system coolant gas line 1360 so that theheat exchange assembly 1300 is connected to the booster box 1102. Then,the DGM system 1000 controls the booster box 1102, so that cold gas 1390is introduced into the droplet generator 115 to cool the temperature inthe orifice of the droplet generator 115. In such an embodiment, the DGMsystem 1000 closes the system heated gas line 1460 to isolate the airheating assembly 1400 from the dual temperature three-way valve 1216 ofthe gas supply unit 1200.

As shown in FIG. 6C, when the droplet generator 115 needs to be heatedup, the DGM system 1000 turns on the air heater 1420 of the air heatingassembly 1400 and switches the dual temperature three-way valve 1216from the system coolant gas line 1360 so that the heat exchange assembly1300 is not connected to the booster box 1102. Then, the DGM system 1000controls the booster box 1102, so that hot gas 1490 can be introducedinto the orifice 155 to increase the temperature in the orifice of thedroplet generator 115. In such an embodiment, the DGM system 1000 closesthe system coolant gas line 1360 to isolate the heat exchange assembly1300 from the dual temperature three-way valve 1216 of the gas supplyunit 1200.

As shown in FIG. 6D, when the droplet generator 115 is refilled with tin(Sn) and is about to pressurized the refilled tin, the DGM system 1000turns on the air heater 1420,so that the DGM system 1000 allows the hotgas 1490 to be introduced into the orifice 155 of the droplet generator115. The DGM system 1000 closes the system coolant gas line 1360 toisolate the heat exchange assembly 1300 from the dual temperaturethree-way valve 1216 of the gas supply unit 1200.

FIG. 7 illustrates a flow chart of a method 1000 for controlling thedroplet generator maintenance (DGM) system 1000 in accordance with anembodiment of the present disclosure. Tin is supplied to the reservoir150 shown in FIG. 3 the by pressuring the droplet generator DG. Then,the EUV lithography process is performed.

The method includes, at S1010, determining whether tin stored in thedroplet generator DG is below a threshold level. If a level sensordetects that the stored tin is below the threshold level, at S1020, thedroplet generator DG is depressurized. When the droplet generator DG isdepressurized, at S1030, the booster box is pressurized to introducecold gas into the droplet generator DG. In some embodiments, the coldgas is a forming gas. In some embodiments, the temperature of the coldgas ranges from about −40° C. to about 0° C. The cold gas is at a lowertemperature than the droplet generator. When the cold gas is filled inthe droplet generator DG, at S1040, the booster box is depressurized sothat hot gas can be exhausted from the droplet generator DG.

At S1050, the temperature is measured to determine whether a temperatureof the droplet generator DG is within an acceptable temperature range(i.e. between about 5° C. and about 50° C.). In some embodiments, theacceptable temperature range is between about 5° C. and about 50° C. Insome embodiments, the temperature measured by a temperature sensor ofthe droplet generator DG indicates a performance of the gas supply unit1200. In some embodiments, the temperature sensor includes a logiccircuit that is programmed to generate a signal when a detectedvariation in temperature measurement is not within an acceptable range.For example, a signal is generated when the detected variation intemperature is less than a certain threshold value. The threshold valueof variation in temperature measurement is, for example, an expectedminimum variation in temperature measurement of the gas supply unit1200. If the measured temperature of the droplet generator DG is notwithin the acceptable temperature range, configurable parameters of theDGM system 1000 are automatically adjusted to repeat the operations ofS1030, S1040 and S1050, so as to reduce the temperature of the dropletgenerator DG to within the acceptable temperature range.

When the temperature of the droplet generator DG is within theacceptable temperature range, the droplet generator maintenance (DGM) isperformed at S1060 by refilling tin into the droplet generator DG orreplacing the droplet generator with a new droplet generator DG. Whenthe droplet generator maintenance (DGM) is completed, at S1070, the DGMsystem 1000 performs a droplet generator heating process, method 1200,as shown in FIG. 9 to bring the droplet generator DG up to its operatingtemperature. When the droplet generator heating process is completed,the droplet generator DG is pressurized at S1080.

FIG. 8 illustrates a flow chart of a method 1100 for controlling thedroplet generator maintenance system to perform the droplet generatorcooling process in accordance with an embodiment of the presentdisclosure. The method includes, at S1110, depressurizing the dropletgenerator DG and turning on a heat exchanger 1320 of a heat exchangeassembly 1300. Then, at S1120, the booster box is pressurized tointroduce cold gas into the droplet generator DG. When the cold gas isfilled in the droplet generator DG, at S1130, the booster box isdepressurized so that hot gas can be exhausted from the dropletgenerator DG. At S1140, the temperature is measured to determine whethera temperature of the droplet generator DG is within an acceptabletemperature range (i.e. from about 5° C. to about 50° C.). If themeasured temperature of the droplet generator DG is not within theacceptable temperature range, configurable parameters of the DGM system1000 are automatically adjusted to repeat the process of S1120, S1130and S1140, so as to reduce the temperature of the droplet generator DGwithin the acceptable temperature range. When the temperature of thedroplet generator DG is within the acceptable temperature range, themethod continues a predetermined process A.

FIG. 9 illustrates a flow chart of a method 1200 for controlling thedroplet generator maintenance system to perform the droplet generatorheating process in accordance with an embodiment of the presentdisclosure. The method includes, at S1210, turning on the heatingelement 505 inside the droplet generator DG as shown in FIG. 3B, turningon a heat exchanger of a heat exchange assembly, and switching the dualtemperature three-way valve 1216 to the system heated gas line 1460 sothat the air heating assembly 1400 is connected to the booster box 1102.In some embodiments, the DGM system 1000 further controls the boosterbox 1102 so that the hot gas 1490 can be introduced into the orifice 155to heat up the droplet generator 115. In some embodiments, the systemcoolant gas line 1360 is closed to isolate the heat exchange assembly1300 from the dual temperature three-way valve 1216 of the gas supplyunit 1200, at S1210.

Then, at S1220, the booster box is pressurized to introduce hot gas intothe droplet generator DG. When the hot gas fills the droplet generatorDG, at S1230, the booster box is depressurized so that cold gas can beexhausted from the droplet generator DG. At S1240, the temperature ismeasured to determine whether a temperature of the droplet generator DGis within an acceptable temperature range (i.e. from about 235° C. toabout 300° C.). If the measured temperature of the droplet generator DGis not within the acceptable temperature range, configurable parametersof the DGM system 1000 are automatically adjusted to repeat the processof S1220, S1230 and S1240, so as to increase the temperature of thedroplet generator DG within the acceptable temperature range. When thetemperature of the droplet generator DG is within the acceptabletemperature range, the method continues a predetermined process B.

Embodiments of the present disclosure provide the benefit of reducingdowntime during maintenance and servicing of EUVL tools. Thus, the EUVLtool is more efficiently used.

An embodiment of the disclosure is a method of servicing a dropletgenerator for a photolithographic apparatus, in which thephotolithographic apparatus comprises a droplet generator maintenancesystem operatively communicating with a droplet generator and having acoolant distribution unit, a gas supply unit and a supporting member.The coolant distribution unit provides a pressurized gas from a boosterbox of the coolant distribution unit to an orifice of the dropletgenerator. The gas supply unit includes a heat exchange assembly and anair heating assembly, and the supporting member that includes athree-way valve and a dual temperature three-way valve. The methodincludes determining whether tin stored in the droplet generator isbelow a threshold level. When the tin stored in the droplet generator isbelow the threshold level, the droplet generator is depressurized. Then,a booster box of the coolant distribution unit is pressurized tointroduce a cold gas at a temperature lower than the droplet generator.In such embodiment, the cold gas introduced into the droplet generatorabsorbs heat from the droplet generator and becomes hot gas.Subsequently, the booster box is depressurized to exhaust the hot gasfrom the droplet generator. Then, temperature of the droplet generatoris measured to whether a temperature of the droplet generator is withinan acceptable cold temperature. When the temperature of the dropletgenerator is within the acceptable cold droplet generator temperaturerange, a droplet generator maintenance is performed. Then, the dropletgenerator is heated. Subsequently, the droplet generator is pressured.

In some embodiments, the cold gas is in a temperature range from 0° C.to 50° C. In some embodiments, the booster box of the coolantdistribution unit is re-pressurized to introduce the gas into thedroplet generator. In some embodiments, when the temperature of thedroplet generator is not within the acceptable cold droplet generatortemperature range, the droplet generator is depressurized and a heatexchanger of the heat exchange assembly is turned on. In someembodiments, after the turning on a heat exchanger of the heat exchangeassembly, the booster box of the coolant distribution unit ispressurized to introduce the gas into the droplet generator. Then, thebooster box is depressurized to exhaust the gas from the dropletgenerator. Subsequently, a temperature of the droplet generator ismeasured to determine whether the temperature of the droplet generatoris within the acceptable temperature range. In some embodiments, whenheating the droplet generator, a heating element inside the dropletgenerator is turned on. Then, a heat exchanger of the heat exchangeassembly is turned on. Subsequently, the dual temperature three-wayvalve is switched to a system heated gas line of the air heatingassembly. In some embodiments, the booster box of the coolantdistribution unit is pressurized to introduce hot gas in a temperaturerange from 235° C. to 300° C. into the droplet generator. Then, thebooster box is depressurized to exhaust gas from the droplet generator.Subsequently, a temperature of the droplet generator is measured todetermine whether a temperature of the droplet generator is within anacceptable hot droplet generator temperature range from 235° C. to 300°C. In some embodiments, pressure at the droplet generator is monitored.Then, the pressure monitored is determined whether the pressure at thedroplet generator is above a pressure threshold. When the pressure atthe droplet generator is above the pressure threshold, an ambienttemperature gas is introduced into the orifice of the droplet generator.In some embodiments, the gas is a forming gas. In some embodiments, theacceptable cold droplet generator temperature ranges from 5° C. to 50°C. In some embodiments, when the tin stored in the droplet generator isbelow the threshold level, clean dry air (CDA) is provided to thebooster box of the coolant distribution unit to control the pressure ofthe droplet generator while depressurizing the droplet generator. Insome embodiments, when the droplet generator maintenance is performed,the tin is refilled in the droplet generator or the droplet generator isreplaced with a new droplet generator. In some embodiments, when the tinstored in the droplet generator is below the threshold level, a forcedair flow is provided by an air conditioning device from a top to abottom of the droplet generator to cool the droplet generator whiledepressurizing the droplet generator.

Another embodiment of the disclosure is a photolithographic apparatusthat includes a droplet generator and a droplet generator maintenancesystem. The droplet generator maintenance system includes a coolantdistribution unit, a gas supply unit, and a supporting member. Thecoolant distribution unit is configured to provide a pressurized gasfrom a booster box of the coolant distribution unit to an orifice of thedroplet generator. The gas supply unit includes a heat exchange assemblyand an air heating assembly. The supporting member includes a three-wayvalve and a dual temperature three-way valve. In some embodiments, thecoolant distribution unit is configured to reduce the temperature of thedroplet generator to within an acceptable range. In some embodiments,the coolant distribution unit is configured to provide clean dry air tothe booster box of the coolant distribution unit to control the pressureto the droplet generator. In some embodiments, the heat exchangeassembly is configured to extract heat from hot gas and to decrease thetemperature of the gas prior to entering the booster box of the coolantdistribution unit. In some embodiments, the air heating assembly isconfigured to provide heat to cold gas and to increase the temperatureof the gas prior to entering the booster box of the coolant distributionunit.

According to another aspect of the present disclosure, aphotolithographic apparatus includes a droplet generator; a dropletgenerator maintenance system; and a controller communicating with thedroplet generator maintenance system. The droplet generator maintenancesystem operatively communicates with a droplet generator. The dropletgenerator maintenance system includes a coolant distribution unit, a gassupply unit, and a supporting member. The gas supply unit includes aheat exchange assembly and an air heating assembly. In some embodiments,the droplet generator maintenance system is further configured tomonitor temperature measured by a temperature sensor of the dropletgenerator. In some embodiments, the droplet generator maintenance systemis further configured to monitor pressure measured at the dropletgenerator, and determine whether to introduce an ambient temperature gasinto an orifice of the droplet generator.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method of servicing a photolithographicapparatus, wherein the photolithographic apparatus comprises: a dropletgenerator; and a droplet generator maintenance system operativelycommunicating with a droplet generator and having a coolant distributionunit and a gas supply unit, wherein the coolant distribution unitincludes a booster box configured to provide a pressurized gas to thedroplet generator, and the gas supply unit includes a heat exchanger andan air heating assembly, the method comprising: upon determining thatthe tin stored in the droplet generator is below a threshold level,depressurizing the droplet generator; pressurizing the booster box tointroduce a cold gas at a temperature lower than the droplet generator;depressurizing the booster box to exhaust a heated gas from the dropletgenerator; and upon determining that a temperature of the dropletgenerator is within an acceptable cold droplet generator temperature,performing a droplet generator maintenance.
 2. The method of claim 1,wherein the cold gas is in a temperature range from 0° C. to 50° C. 3.The method of claim 1, further comprising, upon determining that thetemperature of the droplet generator is not within the acceptable colddroplet generator temperature range, depressurizing the dropletgenerator and turning on the heat exchanger.
 4. The method of claim 3,further comprising: after the turning on the heat exchanger,pressurizing the booster box to introduce the cold gas into the dropletgenerator; and depressurizing the booster box to exhaust the heated gasfrom the droplet generator.
 5. The method of claim 1, furthercomprising: turning on a heating element inside the droplet generator;turning on the heat exchanger; and switching a valve to a system heatedgas line of the air heating assembly.
 6. The method of claim 5, furthercomprising, after switching the valve: pressurizing the booster box tointroduce a hot gas in a temperature range from 235° C. to 300° C. intothe droplet generator; depressurizing the booster box to exhaust the hotgas from the droplet generator; and determining whether the temperatureof the droplet generator is within an acceptable hot droplet generatortemperature range of from 235° C. to 300° C.
 7. The method of claim 6,further comprising: monitoring pressure at the droplet generator; andupon determining that the pressure at the droplet generator is above apressure threshold, introducing an ambient temperature gas into theorifice of the droplet generator.
 8. The method of claim 1, wherein thecold gas is a forming gas.
 9. The method of claim 1, wherein theacceptable cold droplet generator temperature ranges from 5° C. to 50°C.
 10. The method of claim 1, further comprising: Upon determining thatthe tin stored in the droplet generator is below the threshold level,providing clean dry air to the booster box to control the pressure ofthe droplet generator while depressurizing the droplet generator. 11.The method of claim 1, wherein performing the droplet generatormaintenance comprises refilling the tin in the droplet generator orreplacing the droplet generator with a new droplet generator.
 12. Themethod of claim 1, further comprising: upon determining that the tinstored in the droplet generator is below the threshold level, providinga forced air flow by an air conditioning device from a top to a bottomof the droplet generator to cool the droplet generator whiledepressurizing the droplet generator.
 13. A photolithographic apparatus,comprising: a droplet generator; a coolant distribution unit includingfrom a booster box configured to provide a pressurized gas to thedroplet generator; a gas supply unit including a heat exchange assemblyand an air heating assembly; and a three-way valve coupling the coolantdistribution unit to the heat exchange assembly and the air heatingassembly.
 14. The photolithographic apparatus of claim 13, wherein thecoolant distribution unit is configured to reduce a temperature of thedroplet generator to within an acceptable cold droplet generator range.15. The photolithographic apparatus of claim 13, wherein the coolantdistribution unit is configured to provide clean dry air to the boosterbox of the coolant distribution unit to control pressure to the dropletgenerator.
 16. The photolithographic apparatus of claim 13, wherein theheat exchange assembly is configured to extract heat from a hot gas andto decrease a temperature of the hot gas prior to entering the boosterbox of the coolant distribution unit.
 17. The photolithographicapparatus of claim 13, wherein the air heating assembly is configured toprovide heat to a cold gas and to increase a temperature of the cold gasprior to entering the booster box of the coolant distribution unit. 18.A photolithographic apparatus, comprising: a droplet generator; adroplet generator maintenance system; and wherein the droplet generatormaintenance system operatively communicates with the droplet generator,and comprises: a coolant distribution unit to provide a pressurized gasto the droplet generator; and a gas supply unit including a heatexchanger and an air heating assembly, and the droplet generatormaintenance system is configured such that a heat exchanged gas thatpasses through the heat exchanger is provided to the coolantdistribution unit and is pressurized at the coolant distribution unit.19. The photolithographic apparatus of claim 18, wherein the dropletgenerator maintenance system is further configured to monitortemperature measured by a temperature sensor of the droplet generator.20. The photolithographic apparatus of claim 18, wherein the dropletgenerator maintenance system is further configured to monitor pressuremeasured at the droplet generator, and determine whether to introduce anambient temperature gas into an orifice of the droplet generator.